1. Field of the Invention
The present invention relates to a method for manufacturing ice containing carbon dioxide which is suitable for drinks.
2. Description of the Prior Art
Ice containing carbon dioxide as well as carbonic acid drinks much pleases its users with refreshment. However, since water has generally a feature of excluding impurities during its conversion to ice, being frozen, a high concentration of carbon dioxide as impurities in the ice is extremely hard to be included in the ice. Therefore, various technologies for manufacturing ice containing carbonic acid or carbon dioxide have been studied. In a Japanese Patent Application Laid Open No. 29961/81, for example, there is disclosed an apparatus for manufacturing ice containing carbonic acid or carbon dioxide which comprises a cylinder and means for discharging outwardly manufactured ice, means for supplying carbon dioxide, means for agitating contents and means for cooling said contents from the outside which are attached to said cylinder. In said apparatus, ice containing carbonic acid or carbon dioxide is manufactured by charging water and carbon dioxide gas into said cylinder and by cooling said water and carbon dioxide being, while agitating, to a temperature of from approximately -10.degree. to -20.degree. C.
There are, however, the following problems in said prior art.
(1) Transparent ice cannot be obtained since the ice becomes cloudy due to carbonic acid or carbon dioxide in the form of bubbles present in the ice.
(2) A high concentration of carbon dioxide cannot be included in ice.
(3) Most of carbon dioxide bubbles in ice gather on grain boundaries of ice crystals. In consequence, carbon dioxide goes easily out of the ice through the grain boundaries at of elevated temperature of the ice. Accordingly, it is impossible to keep stably the carbon dioxide in the ice for a long period of time.
Carbon dioxide molecules need to be present in crystal lattices so that a high concentration of the carbon dioxide can be contained in ice. In order that the carbon dioxide molecules can be present in crystal lattices, it is conceivable to substitute water molecules of ice for carbon dioxide molecules or to put the carbon dioxide molecules among the crystal lattices of ice. Even in use of such a way, a high concentration of the carbon dioxide cannot be included in ice.